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CURRENT TRANSFORMERS OSKFCURRENT TRANSFORMERS OSKF

GRID

For years, network managers have trusted our OSKF current transformers and thousands are installed in substations around the world. Our customers recognize our top-of-the-line CTs for their long-term strength, safety and reliability for system voltages up to 800 kV.

Customer Benefi ts• Extensive fi eld experience,

including highly seismic regions

• Special accuracy classes for protection: TPS, TPX, TPY, TPZ, PR

• Mineral oil-fi lled: no PCB• Operational security• Stable accuracy over a long

period of time• Built for long life with near

zero maintenance

INSTRUMENT TRANSFORMERS

Metering – Protection

Performance: - Un: 72.5 to 765 kV- In: up to 5000 A- In short-circuit: up to 80 kA1” (Isc dyn: 200 kA peak)- Secondary cores: up to 8

Characteristics: - High quality paper-oil insulation- Top core design with metal head- Oil expansion by stainless steel diaphragm bellows- Oil level indicator- Secondary cores in aluminum box- Changing of primary ratio by primary series-parallel connection (double or triple ratio)

or by secondary taps.

Seismic withstand capability: standard design up to 0.5 g (higher values on request)

Compliance with IEC, ANSI/IEEE or equivalent standards. Other standard on request.

OSKFCurrent Transformers72.5 kV to 765 kV

Designed to meet our customers highest expectations

Long service life and near zero maintenance

OSKF current transformers have been designed for a 30 year lifetime and, thanks to the soundness of our technical concepts, many well out-live this service life.

They have near-zero maintenance requirements: the oil is hermetically sealed from the air by a stainless steel diaphragm assembly and all external parts are of corrosion-resistant material.

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CURRENT TRANSFORMERS OSKF

Linking the power chain

1. Diaphragm bellows2. CT cores3. HV primary terminal4. Primary conductor assembly5. Head housing6. Core housing7. Porcelain insulator8. Bushing tube9. Capacitive grading layers10. Secondary terminal blocks11. Fault current carrying connector to ground12. Ground pad13. Secondary terminal box14. Base assembly15. Sealing plate

Top core design and primary windings

The ‘inverted CT’ design, with active parts in the head, offers particular advantages for higher currents. The primary is normally a straight bar type conductor.

Ratio change can be accomplished either by primary series-parallel connection (double or triple ratio) or by secondary taps. Combinations of series-parallel connection and secondary taps are also possible. This maintains the output and accuracy of the secondaries at all ratios.

The top core design also has the advantage of spreading the primary winding in a uniform and symmetrical way around the cores, avoiding local saturation and reducing the leakage flux.

Cores and secondary windings

Current transformers can have several toroidal laminated cores which are independent of each other. The cores with the secondary winding are accommodated in a thick-walled, round core aluminum protection.

The core housing is connected to a strong metal pipe inside the insulator which leads to the base plate. Cross sections and connections have been dimensioned in such way that the current can be led to the ground in case of internal failure, avoiding an arc inside the insulator.

High quality paper-oil insulation

Insulating paper is applied to the core housing and its supporting tube by a special wrapping machine to ensure high density and uniform insulation.

An extremely low residual humidity is obtained by a special paper insulation drying process.

Grading layers with well-rounded edges give a uniformly distributed field over the entire unit.

Only the highest quality mineral oil with excellent durability and gas-absorbing properties is used. The insulating oil contains no PCB.

Controlled vacuum and temperature treatments withdraw humidity and gas from the paper insulation and insulation oil; the impregnation process results in a high-grade dielectric system.

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CURRENT TRANSFORMERS OSKF

Hermetically sealed for long life

The OSKF maintains a completely sealed and pressure free system through the use of a stainless steel metallic diaphragm assembly. The diaphragm assembly provides oil expansion and pressure compensation, protects the interior from air and moisture and preserves the dielectric strength of the unit. The movements of the diaphragm assembly are translated to an indirect oil level indicator which is visible behind a window in the diaphragm cover.

Leakproof design

The head housing is made of corrosion-proof aluminum alloy. Every housing is subjected to a vacuum leak test by helium leak detection. An overall leak test is performed on every completely assembled unit before oil filling.

Primary terminals

The standard primary terminals consist of aluminum flat terminal pads with 4, 6, 8, or more holes. On request, single or double round terminals made of nickel-plated-copper can be provided.

Secondary terminal box

The terminal box is very spacious and has a removable plate located at the bottom which allows for in-factory or on-site drilling of the conduit entrances for the insertion of cable glands as desired.

Insulator

The outer insulation consists of high-quality oxide porcelain in brown (RAL 8016) or grey (ANSI 70). Standard creepage distances are available according to the dimension tables. Larger creepage distances and composite insulators are available on request.

Protection against bursting

The optimized insulation structure and appropriate structural measures secure the high-grade dielectric for a very long time. The following additional measures are taken to prevent the porcelain from bursting in the event of an inner insulation breakdown, e.g., in case of lightning strikes:

• The active part is above the porcelain in an aluminum head housing.

• An internal fault current connection is provided between the core housing and the ground terminal on the base.

• A pressure relief plate exists in the area of the expansion body on the head.

• Upon request, a composite insulator consisting of fiberglass reinforced pipe and silicone rubber screens can be provided instead of the porcelain insulator.

Earthquake-proof design

The standard OSKF resists medium intensity seismic events. More stringent seismic design requirements can be met upon special request.

Testing

Testing is in conformance with national and international standards. Along with the power-frequency test, capacitance, dielectric loss factor and inner partial discharges are also measured as routine tests. Tests certificates are issued and supplied with the equipment.

Additional information

Dielectric loss factor:

Tan δ smaller than 0.005 up to the power-

frequency test voltage

Radio Influence Voltage (RIV):

Less than 2500 µV at A.1 Um

Internal partial discharge:

Less than 10 pC at 1.2 Um

Frequency:

50 Hz or 60 Hz or 16 2/3 Hz.

Other value on request.

Ambient temperature:

-35°C….+40°C on a 24h average.

Other designs can be provided upon request

for temperatures ranges falling outside of the

mentioned range, i.e. -50°C to +50°C

Mechanical strength:

According to IEC 60044-1.

Other values on request.

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CURRENT TRANSFORMERS OSKF

Dimensions

TypeOSKF 72.5

OSKF 123

OSKF 145

Head size 1 1 3A 3A

Maximum system voltage (Um) kV 72.5 123 123 145

Impulse test voltage (BIL) kV 350 550 550 650

Standard creepage distance (*) mm 1440 2590 3520 3625

Dimensions mm A 1630 2055 2395 2395

B 1260 1690 1900 1900

C 590 1020 1125 1125

D 260 260 285 285

E 740 740 900 900

F 450 450 450 450

Total weight (approx.) kg 245 285 490 495

Weight of oil (approx.) kg 43 49 105 104Indicatives value only - All indicated dimensions must be confi rmed with order.(*) - Standard creepage distance (mm) - Other value on request.

Dimensions

Type OSKF 170 OSKF 245 OSFK 362 OSKF 420 OSKF 550 OSKF 765

Head Size 3A 3A 3A 4 3A 4 5 4 5 6

Maximum system voltage (Um) kV 170 245 362 362 420 420 420 550 550 765

Impulse test voltage (BIL) kV 750 1050 1300 1300 1425 1425 1425 1800 1800 2100

Standard creepage distance (*) mm 4425 5170 7900 7900 9960 9960 9960 11800 11800 13180

Dimensions mm A 1620 3530 4525 4800 5275 5590 5970 6035 6500 7420

B 2120 2900 3890 3965 4635 4755 4815 5200 5340 6050

C 1350 2030 3025 2995 3765 3765 3765 4210 4210 4720

D 285 385 385 330 375 370 370 370 370 480

E 900 900 900 935 900 935 1075 935 1075 1210

F 450 600 600 600 900 900 900 900 900 1200

Total weight (approx.) kg 505 775 1010 1270 1395 1620 1950 1900 2450 3700

Weight of oil (approx.) kg 108 190 225 295 340 420 520 450 550 900Indicatives value only - All indicated dimensions must be confi rmed with order.(*) - Standard creepage distance (mm) - Other value on request.

Inquiry check list

Applicable standards

Rated frequency

Highest system voltage

Test voltages (power frequency, lightning impulse)

Primary/secondary rated currents

Short time current and duration

Core rating (burden, accuracy)

Environmental conditions (altitude, temperatures, pollution, seismic conditions…)

Options:- Composite insulator- Surge arrester on secondary winding- Ground cable connector- Primary terminal- Specific design for use in highly active seismic regions

Available accessories:

- Tg δ tap

- Oil sampling valve

- Lifting bar

- Oil sampling tools kit

- Shock indicators during shipment

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Dimensions

The following dimensions refer to standard versions. Other Um values affect other dimensions.

The head size can change, depending on the core data and the primary nominal current. With regard to the creepage distance and clearance, the insulator can be adapted to the customers’ request.

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Alstom Grid Worldwide Contact Centre www.grid.alstom.com/contactcentre Tel.: +44 (0) 1785 250 070 www.grid.alstom.com

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